FIELD BIOASSAY METHODOLOGIES FOR THE DETECTION OF RESISTANCE TO ACARICIDES IN POPULATIONS OF EUROPEAN RED MITE (ACARI: TETRANYCHIDAE)

Abstract

AbstractThe toxicity of dicofol, pyridaben, formetanate HCl, and abamectin to European red mite, Panonychus ulmi (Koch), was determined using either a Petri dish or leaf dip bioassay (as potential field assay procedures) and was compared with results from a standard laboratory procedure that requires a Potter spray tower to treat leaf disks. Abamectin and pyridaben were the most toxic acaricides tested, and dicofol and pyridaben were more toxic when applied to Petri dishes than to leaf disks. Formetanate HCl was the least toxic acaricide tested by either leaf disk or leaf dip procedures. Diagnostic concentrations of pyridaben were determined as 5 mg active ingredient per litre (a.i./L) with the Petri dish assay and 15 mg a.i./L with the leaf disk assay. Mortality of European red mites to pyridaben at diagnostic concentrations was consistently 100% with the leaf disk assay and > 90% with the Petri dish assay. Residues of pyridaben on Petri dishes stored at 4 °C in a refrigerator were stable for at least 21 d. For dicofol, both leaf disk and Petri dish assays gave similar results, and 25 mg a.i./L, previously used as the diagnostic concentration in the Petri dish assay, resulted in > 99% mortality of the standard susceptible strain. This technique identified resistant individuals in all of the field populations tested. Abamectin applied at 2 mg a.i./L to leaf disks consistently gave 98–100% mortality, but results at 2 mg a.i./L with the Petri dish assay gave variable results and this was not a reliable technique for monitoring resistance. Concentrations of formetanate HCl required for the leaf dip assay were too high to be useful in field assays; however, all populations of European red mite tested using the leaf disk assay appeared susceptible. For the ovicide, clofentezine, mortality of eggs tested by the leaf disk assay at 100 or 500 mg a.i./L ranged from 89 to 100%. Results with the leaf dip procedure, using a 350 mg a.i./L suspension consistently resulted in > 96% mortality of eggs from susceptible field populations. These procedures are a useful tool in the development of resistance management programs for acaricides used in integrated pest management (IPM) systems for tree fruits.